The Spiral Of Death: Why Some Army Ants Commit Suicide

Army ants are divided into two classes: Old World army ants and New World army ants. Old World army ants are native to central and east Africa and the tropical parts of Asia. New World army ants are native to North America, Central America, and South America. Army ants are intimidating predators. They eat smaller insects, seeds, oil, and bread. However, the name, army ant, comes, not from the ants’ hunting practices, but from their aggressiveness while marching. During their nomadic phase, marching army ants will cut, bite, or crush any forestry in their path.

Though they march silently, other animals can sense their approach because of how quickly they destroy any surrounding habitats. [If these mandibles do not make the army ants formidable predators, it’s only because they aren’t used for eating. Although they are omnivores, army ants can only consume liquid through their mandibles.] Unlike most breeds of ants, army ants do not make permanent ant hills. Instead, they make temporary habits by uniting their mandibles and their feet in a formation called a bivouac. When they are ready to leave a particular site, they simply disentangle from one another and keep marching. Their capacity for disciplined, relentless marching is the inspiration for their name, since human military soldiers also possess that ability.

Like soldiers, army ants also act as a unit to effectively defend their own. In order to capture fleeing prey, army ants utilize two types of attacks. In an aptly named swarm attack, a swarm of army ants suprises its potential prey from the front. In a raid attack, the army ants form small clusters and attack their potential prey from various directions. A human observer would see a rapidly marching swarm in front, with diverging clusters of army ants tearing up prey to be carried to a site during their next stationary phase. Based on this information, the aforementioned simile may seem unconvincing. How could these aggressive, efficient army ants ever remind one of workers performing repetitive tasks at unfulfilling jobs for no reward? If that simile applies at all, it isn’t because of how army ants live. It is because of how they could possibly die.

An army ant formation is a colony separated by clusters. There are three primary clusters: the queens, the drones, and the workers. The queens are females who lay eggs. The drones are males who mate with the colony’s queens. The workers are females who capture and deliver prey, move eggs, and protect the colony. Worker army ants have no ability to form visual images, although they can differentiate light from darkness. Worker army ants don’t see their way, they smell it. They communicate and navigate using various pheromones they lay on the ground while marching. If enough worker army ants lose a scent, they lose their ability to navigate. Then each ant (literarily) blindly follows the one immediately in front, forming a spiral that is called an ant mill. Unlike a human, an army ant does not have the cognitive ability to deliberately contemplate or commit suicide. However, army ants who can no longer follow the pheromones they they have laid to guide the colony—for example, army ants who have become entrapped in an enclosed space, either naturally or due to human intervention—will march in a circle until each member of the colony dies of exhaustion.

Check out the video below of it in action:

When a colony is functioning well, army ants can efficiently travel long distances. For example, a raid may be fifteen yards across, and it can contain one hundred thousand (or more) army ants. In an ant mill, the same ability to repeatedly perform the same action, marching, for a long period of time creates an inexorable death march. The longest ant mill discovered to date was one thousand two hundred feet in diameter, and each ant completed a circuit every two and a half hours.

Of course, an ant mill caused by human intervention will not form if the human declines to interfere with the activities of an army ant colony. A naturally occurring ant mill, on the other hand, cannot be prevented or broken once the worker army ants become disoriented. From the anthropomorphic perspective of a human observer, the army ants’ death might seem fated. In reality, natural selection has ensured the survival of a trait which, in most cases, serves the army ants well. Their ability to repeatedly perform a limited number of tasks efficiently while working in unison promotes the survival of the whole colony. This trait enables them to eat quickly when they are in a nomadic phase and use the entire colony to capture prey. Since the ability isn’t one the army ants have consciously developed, they can’t adapt it to meet a changing circumstance.

Maybe humans are tempted to anthropomorphize other animals because humans want to feel less alone. They want other animals to question the supposed certainties of life and fear the certainty of death. Unlike an army ant, a worker in an unrewarding job can always break the cycle.